Bug report #1574
Displaying ECW raster images is very slow
|Assignee:||Frank Warmerdam -|
|Affected QGIS version:||Regression?:||No|
|Operating System:||Windows||Easy fix?:||No|
|Pull Request or Patch supplied:||Resolution:||worksforme|
|Crashes QGIS or corrupts data:||Copied to github as #:||11634|
I have QGIS 1.0.1 for windows installed from OSGEO4W.
If I try to open a simple ECW (67 MB), QGIS is taking too long to open it (about 30-40 seconds). It seems that it doesn't use overviews anymore.
Warmerdam says from OSGEO4W mailing list:
The ECW driver does not report having any specific overview levels and this defeats certain optimizations in the statistics computation. I believe this has a bad effect when an ecw layer is first added to qgis but browsing after that should be fast. The fix is to make the histogram computing logic smarter (I'm not positive if QGIS is using it's own or GDAL's logic) so that for formats like ECW with "arbitrary overviews" a small overview sample of data will be fetched for statistics. I believe this issue is the same in all modern QGIS+GDAL builds, not just specifically in OSGeo4W or windows.